The era of the automobile has brought about significant environmental problems, one of which is represented by the ever increasing accumulation of scrap tires requiring disposal. Various proposals have been set forth for reducing or eliminating the accumulation of scrap tires such as, for example, reclaiming of the rubber in the tires as a re-usable raw material, burning of the rubber in the tires in power plants, and burying of the tires in conventional drumps and landfills.
Reclaiming of the rubber in the tires for further use as a raw material and buring of the rubber in the tires to generate power represent preferred ways of disposing of scrap tires since they recapture much of the energy originally consumed in the manufacture of the tire. However, as a necessary first step to either reclaiming the tires or burning them, the tires must be cut up into smaller pieces (e.g., rectangular chunks of 3 to 4 inches length on each side) which can be subsequently processed.
Similarly, even where tires are disposed of by burying in dumps or landfills, it is necessary to cut the old tires up into smaller pieces before burying in order to prevent the tires from working their way to the surface over a period of time.
Heretofore various proposals have been made for cutting scrap tires into small pieces, and various commercial models of tire cutting machines and shredders are available on the market. Among these devices are simple shearing mechanisms, in which one sharp-edged blade moves past another in a simple scissor action (for example, as shown in U.S. Pat. Nos. 3,578,252 to J. C. Brewer, 4,338,839 to W. M. Farrell, Sr., et al. and 4,338,840 to W. M. Farrell, Sr., et al.). Other such devices include rotary cutting apparatus wherein one set of shearing edges affixed to a rotor moves past mating, interleaved, rotary edges affixed to another, counter-rotating, parallel rotor forming a rotary scissors (as shown for example in U.S. Pat. Nos. 3,656,697 to D. J. Nelson, 3,727,850 to C. A. Krigbaum and 3,931,935 to M. A. Holman). A third type of commercially available tire cutting machine is one in which rotary cutter blades and corresponding rotary anvils rotate in face-to-face contact with each other to cut the tires therebetween (as shown in U.S. Pat. Nos. 3,817,463 to C. A. Krigbaum, 4,081,143 to A. O. Johnson et al. and 4,180,004 to A. O. Johnson).
Tire cutting devices of the type employing either the simple scissor-blade shearing action or the rotary scissor-blade shearing action, while satisfactory for cutting up thin rubberized or plastic-coated textile sheet materials, are relatively much less satisfactory for cutting heavy vulcanized tires which are assemblies of rubber, wires and cords. One reason for this is that the heavy reinforced rubber resists cutting and develops forces as a result of the shear stress, which forces tend to separate the shearing blades. The separated blades then trap rubber between them and the rubber exerts heavy frictional forces against further passage of the blade.
Thus, cutting devices based on shearing blades (both simple and rotary) can operate effectively only when the blades are sharp-edged and when tight clearances between paired blades are maintained. However, with continued use blade edges dull, tend to separate and then drag rubber between them. The separation thus produced defeats the shearing action and enormously intensifies the energy requirements needed to complete the cut. In practice the frictional forces encountered may be so high as to stop the motor or break the machine. As a result, such machines commonly have clutches or reversing gears to allow removal of the entrapped tire portions and permit a fresh cut. At best, the power requirements are very high when tire cutters of this type are employed.
An additional difficulty with tire cutters of this sort is that they fail to shear cleanly the textile cords or wires in the tires and, instead, strip rubber from such members and rupture the cords or wires by tensile breaks. The chopped pieces are then characterized by having projecting filaments of cord or wire that may extend out four or more inches from the rubber chunk. In some cases whole lengths of wire may be torn from the tire with minimal amounts of rubber attached. Chopped up tire pieces, characterized in this way, are considered unsuitable for a number of commercial uses for which cleanly chopped pieces of tire can be used.
Tire cutting machines employing cooperating rotary blades and rotary anvils represent an improvement over the simple scissor-type blade cutters and the rotary scissor-type blade cutters in that they are capable of cleanly cutting the tire carcass with low power demands and without exposure of significant amounts of projecting wire or cord.
Known forms of rotary blade/rotary anvil types of tire cutters have not been entirely satisfactory for a number of reasons. One reason is that the high compression and close blade approach required to cut tires between a rotary blade and a rotary anvil is difficult to attain and maintain due to bearing slack in the bearings supporting the rolls carrying the blades and anvils. Another reason is that in attempting to avoid the problems due to bearing slack, the rotary blades and anvils have been put into hard, pressing contact with one another, causing excessive wear on both the blades and the anvils and necessitating frequent maintenance at high costs. Alternatively, to cope with the bearing slack problem, stationary tear strip members have been employed adjacent to the rotary blades and anvils, allowing rubber to become trapped between the moving and stationary parts and thereby significantly increasing the power requirements of such devices. Yet another problem associated with the rotary blade/rotary anvil types of tire cutters relates to the design of the specific cutting edges employed on the blades, in that such blades have heretofore not been designed in such a manner as to provide long service wear and improved cutting ability.